1. Field of Invention
This invention relates to a composition for forming molded metal containing articles using a molding feedstock having improved stability.
2. Description of the Related Art
Injection molding is a well known process for forming thermoplastic molded articles, such as plastic bottles or containers. Other types of useful injection molded articles are formed from ceramic powder (ceramic injection molding, or "CIM") or metal powder (metal injection molding, or "MIM"), rather than a thermoplastic material. Powder injection molding generally involves injecting a moldable fluid composition, comprising a combination of a ceramic or metal powder, a gel forming binder and a solvent into a mold of a predetermined shape under conditions sufficient to form a shaped article, referred to as a "green body." For example, see U.S. Pat. No. 5,746,957 which teaches a process for forming ceramic and/or metal articles from a composition comprising a ceramic and/or metal powder, a polysaccharide binder and a gel strength enhancing agent. After forming a green body, it is most typically required to sinter the article to densify the article so that it may have useful strength and other physical and mechanical properties.
There are various reasons for which metal or metal containing, ceramic molded articles may be desirable. For example, a metal article may be highly conductive, or a metal component may impart superior strength or durability to an article. Generally, metal injection molded articles may be formed from any pure metal or metal alloy in powder form. Powder injection molding applications typically use wax or polymeric binders, or a water-based binder and solvent for a variety of metals, for example stainless steels or nickel based superalloys. However, it is well known that certain metals and metal compounds oxidize when contacted with water. For example, iron reacts with water to formiron oxide, or rust, and copper reacts with water to form copper oxide. Therefore, it has been a problem in the art to form metal containing compositions using a water based binder while preventing oxidation of the some metals.
To illustrate, U.S. Pat. No. 6,013,723 teaches a composition for injection molding an article incorporating a fatty acid metal salt lubricant. This lubricant is used to inhibit the formation of rust when iron containing compounds are incorporated within the composition. Also, U.S. Pat. No. 5,906,813 teaches a composition for injection molding an article incorporating an antioxidant additive. This antioxidant is used to inhibit the formation of rust when iron containing compounds are incorporated within the composition. Further, U.S. Pat. No. 5,378,428 provides a method of preserving an article wherein the article and an oxygen absorbent composition are sealed inside a container. The oxygen absorbent composition serves to prevent rusting of the article.